MBE Growth and Characterization of Device-Quality Thick InN Epilayers; Comparison between N-polarity and In-polarity Gro
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MBE Growth and Characterization of Device-Quality Thick InN Epilayers; Comparison between N-polarity and In-polarity Growth Processes Akihiko Yoshikawa1,2,3, Yoshihiro Ishitani1,2,3, Song-Bek Che1,2,3, Ke Xu3, Xinqiang Wang2,3, Masayoshi Yoshitani1, Wataru Terashima1, and Naoki Hashimoto1 1
Department of Electronics and Mechanical Engineering, 2Center for Frontier Electronics and
Photonics, and 3InN-project as a CREST program of JST, Chiba University 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan ABSTRACT Epitaxy of InN films with N-polarity and In-polarity was investigated by RF-MBE with several in-situ monitoring/controlling systems. It was found that the epitaxy temperature for N-polarity growth could be as high as 600 °C and this was about 100 deg higher than that for In-polarity case. This temperature difference in two polarities drastically affected not only the growth behaviors but also the properties of InN epilayers, i.e. N-polarity growth was preferable in both view-points. The step-flow-like surface morphology was achieved for the InN films grown with N-polarity at 580 °C. The FWHMs of X-ray rocking curves for InN (002) and (102) of 5-8 µm-thick InN films grown in N-polarity were about 200-350 and 650-950 arcsec, respectively. The highest Hall mobility was above 2000 cm2/V·s with a background carrier concentration of 1-2×1018 cm-3 at room temperature. For both polarity films, N-rich condition was necessary for the stable InN growth to obtain 5-8 µm-thick InN films. INTRODUCTION Growth of high-quality thick InN epilayer is still a challenge due to its low dissociation temperature (1-9). InN epilayers start to decompose at temperatures above about 500 °C and In-droplets easily appear on the surface. Once those In-droplets appear on the surface, they disturb the epitaxy itself and it is very difficult to continue/keep the growth. The growth process and/or the growth rate are limited by the dissociation of InN itself and not by the re-evaporation of excess In on the surface. This situation is slightly different to the case for other III-nitrides, in particular, MBE of GaN. Because of the much higher thermal stability of GaN than InN, the epitaxy temperature of GaN can be increased to higher temperatures up to 850 °C. Therefore, on the contrary to the epitaxy of InN, the growth process and/or the growth rate of GaN are limited by the effective supply rate of Ga and not by the dissociation of GaN itself. Then excess Ga on the surface can be fairly easily re-evaporated even after the appearance of Ga droplets. Further, its epitaxy can be continued even after the appearance of Ga droplets by carefully adjusting the
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growth conditions so as to enhance the diffusion of N-species in the Ga droplets, resulting in the growth of GaN even beneath the Ga droplets. Anyway, the epitaxy of InN are drastically affected by the low dissociation temperature of InN itself. Until now we have pointed out that the crystalline polarity plays a very important role in the epitaxy control of InN growing on c-plane s
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